The present invention relates generally to the field of digital image enhancement and image processing. More particularly, this invention relates to programmable serial neighborhood transformation processing systems.
Prior art serial neighborhood image processors enhance visual images in digital fashion using various algorithms operating on pixels representing the original image. These image processors first divide the original image into an array of pixels and a digital value is assigned to each pixel based on a luminance scale. The number of pixels for a given area and the range of the luminance scale for each pixel determines the spatial and amplitude resolution for the image processor. The process of converting the original image into a digital representation of the image is done using any device with serial data image conversion. For serial neighborhood transformation processors, the entire image is raster scanned a single line at a time and the serial raster data is fed through an n.times.m neighborhood of pixels. The serial data representing the original image is transformed using the n.times.m neighborhood to perform pattern matching and pattern analysis. The center of the n.times.m neighborhood is used as the transformation point from the neighborhood and a transformation takes place based on the surrounding pixels in the neighborhood.
Image processors are used for a wide variety of sciences including military applications, weather forecasting, automated materials handling, and a host is well suited to digital image processing technology is that of manufacturing defect detection on artwork and layers of printed wiring boards (unpopulated printed circuit boards), hybrid circuits and integrated circuit masks. These last applications use image processing techniques to detect manufacturing defects in the pattern or artwork used for fabricating electronic circuit modules or for detecting flaws in the manufactured circuits. The integrity of these patterns is crucial to the proper operation of the end product and is typically found to be a large percentage of the overall cost of producing electronic circuits and components.
Typical manufacturing defects found on PWB's or wafer masks are mouse bites, pinholes, opens, shorts, cracks, misalignment errors and various other types of problems typically occurring in wiring patterns. The aforementioned terms are terms of art that cause particular types of faults in the electronic components which manifest themselves in various ways. Often several distinct failure detection techniques are required to indicate and isolate the manufacturing defect. Many of the aforementioned manufacturing defects, however, can be detected and isolated by digital image processing techniques by visually scanning the product during manufacturing.
Some of the aforementioned manufacturing defects typically found on PC boards or wafer masks have been postulated to be detectabale using various neighborhood transformation algorithms as described mathematically in an article authored by Jon R. Mandeville found in the IBM Journal of Research and Development, Vol. 29, No. 1, Jan. 1985, pp. 73-86. Various image enhancement algorithms using specific image processing primitives (neighborhood transformations) are described in the article, such as expansion, contraction, thinning and trimming. These image processing primitives when combined for use in feature detection algorithms can be used to identify and locate various faults in artwork. However, the thinning and trimming primitives require several stages of the traditional 3.times.3 neighborhood transforms, resulting in extensive hardware overhead that can be avoided with the present invention.
The present invention improves upon the prior art by combining the use of an extended neighborhood of pixels to achieve single stage thinning and trimming with a more efficient architecture, resulting in lower-cost real time image processing. The present invention relates generally to the improvement of serial neighborhood transformation processors and is not intended to be limited to the particular application of electronic PWB fault detection.